Protection of center-spin coherence by a dynamically polarized nuclear spin core

Understanding fully the dynamics of coupled electron-nuclear spin systems, which are important for the development of long-lived qubits based on solid-state systems, remains a challenge. We show that in a singly charged semiconductor quantum dot with inhomogeneous hyperfine coupling, the nuclear spins relatively strongly coupled to the electron spin form a polarized core during the dynamical polarization process. The polarized core provides a protection effect against the electron-spin relaxation, reducing the decay rate by a factor of N₁, the number of the nuclear spins in the polarized core, at a relatively small total polarization. This protection effect may occur in quantum dots and defect centers in solids, such as nitrogen vacancy centers in diamond, and could be harnessed to implement in a relatively simple way long-lived qubits and quantum memories. ©2010 The American Physical Society